Since the advent of electromobility and the increased use of renewable energies, efforts are made increasingly to seek larger electricity storage solutions. According to the present state of the art, lithium-ion accumulators are most suitable for this because, in comparison with other batteries, they offer relatively high energy density, i.e. charge capacity, relating to the battery weight, but also with respect to the space required. However, there is a partial risk of explosion, so that safety aspects must be given great attention. In addition to this, there are still relatively high costs, at least with today's production possibilities.
One development line is directed to the development of large accumulator cells. However, the size and charge density of such individual battery modules is limited due to the danger of explosion which is to be kept in mind, so that usually several, relatively large cells, fitted with irons which show low susceptibility to explosions and also have a lower charge density, are interconnected with one another. One example of this is shown in German patent application DE 10 2013 203 102 A1, which shows a battery module formed from two battery cells. The two battery cells are connected in series in order to double the voltage supplied, or to halve the potential damage caused by a potential explosion. A further example of a high-voltage battery module, which is constructed from a stack of series-connected frame flat cells, i.e. flatly designed single large-battery cells, can be taken from DE 10 2010 013 034 A1, and a similar module from WO 2011/092039 A1. US patent application US 2006/0246348 A1 is based on an even more extensive modularization. Single prismatic cells are welded to cell strands at their poles. A plurality of individual cell strings accommodated side by side in corresponding holders form a battery module, with the cooling medium flowing around the individual cells, and a housing formed by the interconnected holders.
Due to the limitation of the potential damage caused by the explosion of a single cell and the cost advantages obtainable by mass production, a further developmental direction is directed to the use of relatively small round-wound individual cells arranged in parallel and/or in series in order to manufacture battery modules with the desired high capacity and output voltage. Owing to the relatively controllable risk associated with the failure of a single round cell, ions with relatively high charge densities can be used here, but they are also more susceptible to explosions and would therefore be unsuitable for large battery cells. In the case of small round cells however, they would only lead to outgassing in the case of an explosion, or they would only cause relatively manageable damage in the case of an explosion.
A pioneer who has identified the cost advantages associated with the mass production of round-wound single cells is Tesla. In the Tesla vehicles, battery modules are present in the underbody, which consist of a plurality of battery blocks arranged side by side in a distributed manner and are interconnected by means of intermediate switch lines, wherein each battery block has a layer of upright lithium-ion round cells, see e.g. European patent application EP 2 157 634 A2. Between the round cells of a battery block, cooling lines can be passed through, and the individual round cells are welded together in a relatively complex manner with a conductor wire, which in turn is welded to a conductor rail.
The conductor wire serves as a kind of current limiter in the manner of a fuse. In other words, it is intended to prevent an excessive power output/draw of a single cell and thus its failure or potential explosion. The cooling is intended to counteract the effect that, in the case of failure of individual cells or even in the case of inadequate power output of individual cells, other cells heat up strongly and soon fail or even gas out/explode in the permanent overload.
It is therefore attempted, through the single-wire contact, to achieve a current or voltage output which is as uniform as possible over all round cells in order to prevent the failure of individual cells, so as not only to obtain the capacity and output voltage of the battery module or of a single battery block of the module, but in order to not irreversibly damage the entire block or the entire module when the cells still operating are overloaded and overheated as a result of the failed cell.
Due to the standing arrangement of the round cells in the individual blocks and the arrangement of the battery blocks in a plane next to one another, as well as by the cooling lines in the blocks and the space required for the interconnection of the battery blocks and the individual wire contact of the round cells, the space requirement for the overall battery module also increases in combination with decreasing charge capacity relating to the space used for the module and the production costs involved.
US patent application US 2011/0177373 A1 discloses another battery module with a single layer of round cells in a standing arrangement.
Due to the above drawbacks, in the production of multiple round-cell battery modules, a lying arrangement of the round cells in battery blocks is often preferred, wherein the adjoining battery blocks form, in a series circuit and series arrangement, a strand of battery blocks which each comprise a layer of adjacent and stacked round cells which are switched in parallel at their two ends via respective contacts, wherein the battery blocks, which are formed from parallel-connected round cells, are then switched in series in the battery block strand in turn.
Such a battery module is disclosed, for example, in European patent specification EP 2 410 590 B1. A respective plurality of round cells of a block is attached to contact plates by spot welding and is thus connected in parallel. The contact plates are connected via lateral tabs to contact plates of the next level in the battery block strand. The round cells are furthermore accommodated in holders with semi-cylindrical receptacles, wherein the holders comprise through-bores in an axially parallel manner in relation to the round cells, through which tie rods are guided, which are clamped at both ends of the battery block strand and thus hold the battery module together. Further contact plates are inserted between the round cells of a block, which are joined together by spot welding to the contact plates to form a battery block, and the battery block adjoining the latter, in order to connect the battery blocks in series.
A similar battery module is shown in WO 2012/060754 A1 or US 2013/224532 A1 of the same patent family. Several battery packs, which in turn consist of a plurality of parallel-connected round cells, are arranged one behind the other in a battery block strand and are connected in series. The series connection of the battery blocks and the parallel connection of the round cells in each of the battery blocks is effected via perforated metal plates between the battery blocks, wherein nickel strips are pressed into the holes of the metal plates, which are spot-welded there with one pole of a round cell. The same can be gathered from US 2004/0197642 A1. The series connection of two modules consisting of three parallel-connected cylindrical cells is shown there. The parallel and series connection is effected here via contact plates which have square connecting surfaces assigned to the poles of the round cells. In the connecting surfaces, slots are provided, which serve for spot welding with the round cells.
US 2011/0223776 A1 discloses a releasable modular interconnect configured to form releasable electrical connections with a plurality of power cells. The electrical connections are established by pressing contacts with external force onto the poles of the cells. Output buses are positioned to output electricity to output terminals.
WO 2014/125807 A1 or US 2016/0006006 A1 of the same patent family disclose another battery module having a plurality of round cells, which round cells could be grouped into a series of two round cell stacks. The two round cell stacks are arranged in a row and have an equal plurality of round cells, each.
WO 2011/096863A1 shows a battery module with four rows of round cells, the round cells of which are each connected in parallel, wherein the round cell rows are electrically connected in series. Geometrically, the round cell rows are not arranged in series, but on both sides of a printed circuit board. The circuit board contains the battery management. On the printed circuit board, contact plates which protrude at right angles are mounted, which in turn have nickel strips with bent contact surfaces facing the poles of the round cells. Nickel is used in spite of poorer conductivity than copper for example, because, unlike copper, it can be welded with ease. A pure clamping arrangement for contacting the round cell poles instead of the welding with the nickel strips is considered less reliable with regard to the electrical and mechanical connection.
German patent application DE 10 2010 013 003 A1 also shows, in addition to a battery module composed of a stack of flat cells, a battery module which consists of battery packs, each of which is constructed from a layer of lithium-ion round cells, wherein the battery packs in the battery pack row thus formed are re-connected in series by interposed pole plates and the round cells of each battery pack are welded at their two pole ends to the pole plate there and are thus connected in parallel.
The welding of the round cells by laser welding with pole plates etc. at inaccessible locations between the round cells of the battery packs or by spot welding with pole plates using further contacting plates between the battery packs is complicated and also error-prone however.